Relay valve for pneumatic or hydraulic application

ABSTRACT

A valve including a housing in which is disposed a relay piston. The relay piston has an upper control surface adjacent a control chamber leading to a control connection. The underside of the relay piston is in communication with a reaction chamber leading to a working pressure connection. An outlet valve seat is formed on the lower extremity of the relay piston. A multistage hollow graduated piston disposed within a graduated bore formed in the housing. The graduated piston has a tapered edge extending downwardly to form an inlet valve seat. A hollow valve element is cooperatively associated with the inlet and outlet valve seats to form inlet and outlet valves. The underside of the graduated piston a reaction chamber which is connected to a second control pressure connection. A supply pressure connection is connected to an annular chamber which is in communication with the inlet valve so the working pressure is gradually increased in steps until a predetermined pressure value representing an emergency situation is exceeded which causes the working pressure to immediately rise to the full pressure value of the supply pressure.

This is a division, of application Ser. No. 06/828,927, filed Feb. 12,1986, which is a continuation of application Ser. No. 06/679,420, filedDec. 7, 1984, now abandoned.

FIELD OF THE INVENTION

This invention relates to a relay valve for a pneumatic or a hydraulicbraking application for motor and/or trailer vehicles which includesmeans for causing the working pressure to be increased gradually to avalue beyond the delivered control pressure up to the value of theavailable supply pressure.

BACKGROUND OF THE INVENTION

There are certain known relay valves, one of which is shown anddisclosed in published German Patent Application DE-OS 27 03 940. Arelay valve of this type is normally located in pneumatic brakinginstallations for vehicles between reservoir and pneumatic consumers,namely, the brake cylinders. When pressurized with a control pressurewhich is supplied, for example, by a pedal-operated brake valve, anoutlet valve connecting a working connection of the valve with theatmosphere is closed, and an inlet valve connecting a reservoir with theworking connection is opened. Thus, there is a rapid buildup of pressureto the consumers. When the control pressure decreases or disappears, theinlet valve is closed and the outlet valve is opened, whereupon theconsumers are rapidly partly or entirely exhausted to atmosphere.

On such a relay valve, the working pressure exerted and the controlpressure are in a specified pressure ratio to one another based on thedesign of predetermined values established by the ratio of surface areason the relay piston.

There are applications in which the consumers can function with thedesign pressure ratio only in a limited control pressure range, andbeyond that require an increase in the working pressure, up to the fullavailable supply reservoir pressure, which is graduated and more rapidthan that specified by the design pressure ratio.

An example of consumers of this type for motor vehicles withload-controlled brake force controllers is represented by requirementsin several countries regarding such braking action. The requirement inthese countries is that, in emergency situations, the reservoir pressureavailable in the vehicle must be able to be released to the brakecylinders in controllable stages. Ordinarily, the load-controlled brakeforce controllers have a control action with a predeterminedcorrespondence between load status or dynamic axle load and the workingpressure (i.e. brake pressure) released, and therefore cannot be usedfor applications of the type described above.

OBJECTS AND SUMMARY OF THE INVENTION

The problem addressed by the invention is, therefore, the improvement bysimple means of a relay valve of the type described above which makes itpossible to effectively use ordinary load-controlled brake forcecontrollers during pneumatic braking applications for motor vehicles.

The concept and object of the invention is to define an emergencysituation by a predetermined value of a second control pressure, andafter this value is exceeded to the increase of the working brakepressure, and thereby a deflection of the design characteristic of therelay valve in the direction of higher working pressures continues,until the entire available supply reservoir pressure is reached. Toachieve such a characteristic, it is desirable when the second controlpressure defining the emergency situation occurs to increase the controlsurface area of the relay piston, by adding a supplementary surface.

The preferred embodiments of the invention are particularly addressed tothe advantageous manner designing the inlet valve and the outlet valveof the relay valve, and the reaction surface of the relay piston.

This results in an advantageously simple embodiment of the invention,namely, to utilize a predetermined absolute value of the second controlpressure to define the emergency situation.

The definition of the emergency situation may be simply put as apredetermined ratio between the second control pressure and thereservoir pressure whereby, even with a fluctuating reservoir pressure,the advanced control capability of the supply pressure to the brakes isalways guaranteed.

A first preferred embodiment proposes, after the onset of the emergencysituation, the control of the inlet valve and the outlet valve of therelay valve by a second activating means.

A second preferred embodiment proposes that the relay piston be designedas a differential piston with a large control surface and a smallerreaction surface, and that the differential surface be pressurized withthe second control pressure up to a maximum value determined by apressure relief valve. It is apparent that the invention and thepreferred embodiment can also be executed with different configurationsof the relay valve which increase or decrease the pressure.

When the relay valve described by the invention is used in a pneumaticbrake installation for vehicles, the pressure regulated by the brakeforce controller can advantageously be used as the control pressure, andthe unregulated pressure conducted to the brake force controller can beused as the second control pressure.

In addition to the very advantageous application of the relay valve,according to the invention described above in pneumatic brakeinstallations for motor vehicles with load-controlled brake forcecontrollers, the relay valve described by the invention can also be usedvery advantageously, as its properties and characteristics describedbelow show, in other applications. For example, it could be consideredfor use on machine tool controls or railway barrier controls.

Briefly, the invention relates to a relay valve for a pneumatic brakeapplication for vehicles comprising, an inlet valve having a controlconnection which is pressurized with a control pressure and having atleast one supply connection which is put in communication with at leastone working connection, an outlet valve for connecting the workingconnection to atmosphere, said inlet valve and outlet valve beingoperated by a relay piston which can be pressurized by control pressureto move the inlet valve in the opening direction and being operated bythe relay piston which can be pressurized by the working pressuresupplied to a reaction chamber which is connected to the working and tomove the outlet valve in the opening direction, means which provides agraduated increase of the working pressure beyond the valuecorresponding to the delivered control pressure up to the availablesupply pressure, and said means is activated above a predeterminedpressure value of a second control pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject invention will be explained below on the basis of severalembodiments which are illustrated in the drawings.

FIG. 1 shows a relay valve with a deflection characteristic with asecond control apparatus.

FIG. 2 shows a family of characteristic curves of the relay valveillustrated in FIG. 1.

FIG. 3 shows another characteristic of the relay valve illustrated inFIG. 1.

FIG. 4 shows a pneumatic brake installation with a relay valve.

FIG. 5 shows a detail of the characteristics of the pneumatic brakeinstallation illustrated in FIG. 4.

FIG. 6 shows a relay valve with a deflection characteristic with anintegrated pressure relief valve.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and in particular to FIG. 1, there isshown a relay valve in which a second control device is integrated intothe valve housing to obtain the desired response deflectioncharacteristics.

As shown, the housing includes an upper housing portion 3, a middlehousing portion 31, and a lower housing portion 23. A relay piston 35 islocated in housing 3, 23, 31 and is guided so that it can longitudinallymove in a sealed manner. The top of the relay piston 35, along with theunderside of the upper housing portion 3, form a control chamber 4 whichcan be pressurized with a source of suitable control pressure which isconnectable to a control connection 5. The upper side of the relaypiston 35, facing the control chamber 4, is designed and constructed asa control surface 2. The middle housing portion 31 is connected with theupper housing portion 3 in a sealed manner, and the middle housingportion 31 includes a supply connection 27 and a working or operatingconnection 10. The middle housing portion 31 also includes an integralinsert which fits into a multistage graduated bore 8, 14, 15. The uppersmallest diameter 8 is contiguous with a reaction chamber 11, and issituated below the underside of the relay piston 35 which forms areaction surface 34. The lower largest diameter 15 of the graduated bore8, 14, 15 is located in the lower housing portion 23, which is connectedin a well-known, air-tight fashion with the middle housing portion 31.Between the smallest diameter 8 and the largest diameter 15, there issituated a middle diameter 14 of the graduated bore 8, 14, 15. As shown,the graduated bore 8, 14, 15 accomodates a multistage hollow graduatedpiston 16, 24, 25, which is designed to have complementary and matchingdiameters corresponding to the graduated bore. The piston is guided in asealed manner in the bore; that is, the radial outer surfaces of thegraduated piston are sealed against the corresponding surfaces of thebore by suitable sealing rings.

As shown, the upper end of the small diameter portion of the graduatedpiston 16, 24, 25 is formed as an annulus area, which is designed as agraduation surface 32. The hollow circular area portion includes aninternal tapered circumferential depending edge, extending toward theinside of the graduated piston, which serves as an inlet valve seat 7.

It will be seen that a tubular double valve element 9 is disposed on theinside of the graduated piston 16, 24, 25. The tubular double valveelement 9 cooperates with the depending peripheral edge of the inletvalve seat 7. The tubular double valve element 9 includes an upperflange portion, extending radially outwardly, having an outer brimcooperating with the circular inlet valve seat 7 and having an innerbrim cooperating with a uniaxial circular outlet valve seat 6.

The graduated piston 16, 24, 25 consists of three parts; an outer part24, an insert 16, and a guide ring 25.

The double valve element 9 moves, guided in a sealed manner in a guidebore of the guide ring 25, fastened in a sealed manner in the inside ofthe outer part 24 by means of an axial retaining ring.

A closing compression spring 13 is caged between the guide ring 25 andthe flange of the double valve element 9 to urge the double valveelement 9 against the inlet valve seat 7. As shown, the lower internalend with the large diameter portion of the graduated piston 16, 24, 25receives, in a sealed internal manner, the bushing or insert 16, whichis axially fastened in the graduated piston 16, 24, 25 by means of asuitable snap or retaining ring. The large end surface of the graduatedpiston 16, 24, 25 cooperates with a second control surface 21 which actsas a lower stop. Depending downwardly from the graduated piston 16, 24,25, the insert 16 includes a hollow exhaust sleeve 20. The exhaustsleeve 20 is seated in the lower housing portion 23 in a sealed manner.The lower housing portion 23 includes a second control connection 17. Itwill be seen that situated between the reaction surface 34 of the relaypiston 35 and the graduation surface 32 of the graduated piston 16, 24,25, there is defined a reaction chamber 11 which is connected with theworking connection 10.

A depending tappet or stem 33 is formed on the reaction surface 34 ofthe relay piston 35. The lower edge of tappet 33 forms an outlet valveseat 6 which, with the double valve element 9, form an outlet valve 6,9.

The inside of the graduated piston 16, 24, 25 and the inside of thedouble valve element 9 are designed as an exhaust chamber 19. Thus, whenthe outlet valve 6, 9 is open, the reaction chamber 11 is incommunication with the cavity of the exhaust sleeve 20. As shown, arelief or check valve is formed by an elastic diaphragm which is locatedin the lower housing portion 23 and is in communication with theatmosphere.

When the relay valve is used in installations with pressure fluids,other than air, or in a closed circuit, the exhaust chamber 19 may beplaced in communication with an essentially unpressurized reservoir.

The graduations between the small diameter and the middle diameter ofgraduated piston 16, 24, 25 and the graduated bore 8, 14, 15 form anannular chamber 28, which is in communication through a housing duct 29to a supply pressure connection 27.

It will be seen that, located on the inside of the graduated piston 16,24, 25 between the inlet valve 7, 9 and the outer surface of the doublevalve element 9, there is defined a piston supply chamber 30 whichfunctions as a supply chamber. The supply chamber 30 is in communicationthrough passages in the wall of the graduated piston 16, 24, 25 with theannular chamber 28. The step or ledge on part 24 of the graduated piston16, 24, 25, facing the annular chamber 28, is designed as a resetsurface 25a. In the annular chamber 28, there is disposed a returnspring 26 which is gaged between the lower reset surface 25a and anupper step annular ledge formed on the middle housing portion 31 in theannular chamber 28.

In certain applications, which do not have special requirements withrespect to the response behavior of the relay valve, the return spring26 can be eliminated for economic reasons.

In another modified version, the graduated bore 8, 14, 15 and/or thegraduated piston 16, 24, 25 may be designed so that the supply pressureexisting in the annular chamber 28 has no external effect and exerts noforce on the graduated piston 16, 24, 25 in its direction of movement.To accomplish such an operation, the graduated piston 16, 24, 25 couldbe designed with identical-sized upper and lower graduated surfaces inthe annular chamber 28. In such an arrangement, an adjustable controlspring would be located between suitable end or graduation surfaces ofthe graduated bore and of the graduated piston.

The lower housing portion 23 is provided with the second control surface21. A second control chamber 18 is in communication with the secondcontrol connection 17. The surface 21 cooperates with a stop surface 22located on the lower end of the graduated piston 16, 24, 25 to limit thedownward displacement.

The upper housing 3 includes a stop surface 1 by means of which theupward motion of the relay piston 35 is limited as it moves toward theopening direction of the inlet valve 7, 9.

A chamber is formed by the step existing between the medium diameter andlarge diameter bores in the middle housing portion 31. The graduatedpiston 16, 24, 25 is in communication through a square passage formed inthe graduated piston 16, 24, 25 to the exhaust chamber 19.

It is understood that the invention can also be operated with asingle-stage graduated piston and bore without the latter chamber. Also,the invention may be utilized with a graduated piston and bore whichemploys more than two stages.

The presently-described relay valve functions in the following manner.

The annular chamber 28 and the piston supply chamber 30 are constantlypressurized by the supply connection 27 with the supply pressuredelivered by a suitable reservoir (not shown). The supply pressure holdsthe graduated piston 16, 24, 25 against the stop surface 22 and isassisted by the compression spring 26, which applies a force on thelower reset surface 25a.

The control connection 5 and the second control connection 17 are incommunication with a first and second control pressure source,respectively. The two control pressure sources are preferably to becompletely independent of one another. However, when the two pressuresare combined, the pressures in the first and second control connections5 and 17 are identical.

The two control pressure sources can also be related to one another, inwhich case, the first and second control pressures are a given ratio ofone another, which may be also variable. Such a situation occurs whenone of the control pressure sources is derived from the output of aload-controlled brake force controller and the other of the controlpressure sources is taken from the pressure conducted to theload-controlled brake force controller by a brake valve. In this case,the control pressures are in a ratio to one another which is a functionof the control ratio of the load-controlled brake force controller,whereby this ratio varies with the load status and the dynamic axle loadof the vehicle.

Further, one of the control pressures can be omitted entirely. As arule, the control pressure sources and the relay valve are supplied froma common reservoir. However, it is possible to employ separate supplysources.

In the rest position, the outlet valve 6, 9 is opened and the workingconnection 10 is in communication with the atmosphere via the reactionchamber 11 and the exhaust chamber 19. The inlet valve 7, 9 is closed.

Under normal circumstances, both of the control connections aresimultaneously pressurized with the first control pressure and thesecond control pressure. The sequence of operation of the relay valve inthis case is achieved in two operating phases.

In the first operating phase, the graduated piston 16, 24, 25 is heldagainst the stop 22 by reaction forces which are produced by the supplypressure, and by the return spring 26 acting on the reaction surface25a, and by the working pressure which is present in the reactionchamber 11 acting on the graduated surface 32. These reaction forces areoperating against the second control force produced by the secondcontrol pressure on the second control surface.

In an embodiment not illustrated, in which the supply pressure exerts nofree force on the graduated piston in its direction of movement, but thereaction force is simply the effort exerted by the return control springand the force on the step surface 32 which is a function of the workpressure in the reaction chamber 11.

In this first operating phase, the double valve element 9 is activatedexclusively as a function of the equilibrium of forces between thecontrol surface 2 and the reaction surface 34 of the relay piston 35 andthe working pressure conveyed to the working connection 10 isessentially identical to the first control pressure. The double valve 6,7, 9 formed by the inlet valve 7, 9 and the outlet valve 6, 9 bothassume a closed position.

In the described embodiment, the relay valve increases or decreases thepressure and the working pressure in this first operating phase is afunction of the control pressure which is determined by the design.

The second operating phase begins when the reaction force is overcome bythe second control force. The graduated piston 16, 24, 25, at this time,moves upwardly off of the stop 22 into the reaction chamber 11 so thatthe inlet valve 7, 9 is opened by the tappet 33. Thus, additional airpressure now flows from the piston supply chamber 30 into the reactionchamber 11, whereby the working pressure existing in the reactionchamber 11 from the first operating phase undergoes an increase invalue. The equilibrium of forces on the relay piston 35 is therebyremoved, and the relay piston 35 is displaced against the stop 1 on theupper housing portion 3. The graduated piston 16, 24, 25 follows thismovement with an open inlet valve 7, 9. The inlet valve 7, 9 remainsopen until an equilibrium of forces is reestablished on the graduatedpiston 16, 24, 25. The working pressure necessary for this purpose, onaccount of the ratio of surface areas on the graduated piston 16, 24,25, is lower than the second control pressure and higher than the levelof working pressure which corresponds to the control pressure releasedat the control connection 5.

When an equilibrium of forces is achieved, the graduated piston 16, 24,25 moves backward by the closing stroke of the inlet valve 7, 9, and thedouble valve 6, 7, 9 assumes a closed position, in which both the inletvalve 7, 9 and the outlet valve 6, 9 are closed.

For every increase of the second control pressure, the graduated processdescribed above is repeated. In the second phase of operation, theworking pressure released is determined exclusively by the graduatedpiston 16, 24, 25. The control pressure remains completely withouteffect, unless it assumes a higher value than the working pressuredetermined by the graduated piston 16, 24, 25 and if this workingpressure is still less than the supply pressure.

When there is a reduction of the control pressure, the sequence ofoperation described above occurs in the reverse manner.

Referring now to FIGS. 2 and 3, there is schematically shown the typicaloperating characteristic curves of the relay valve described above.

As shown in FIG. 2, the working pressure versus the control pressure isexhibited by the series of plotted curves.

The working pressure, symbolized by P₁₀, is plotted on the ordinate. Thecontrol pressure, symbolized by P₅, is plotted on the abscissa. Thesupply pressure, assumed to be constant, symbolized by P₂₇, is plottedparallel to the abscissa.

The operational behavior of the relay valve is shown for severalconstant ratios of the first control pressure P₅ to the second controlpressure P₁₇, whereby the Line OA₁ B₁ characterizes a small ratio of P₅/P₁₇, Line OA₂ B₂ characterizes an intermediate ratio of P₅ /P₁₇, LineOA₃ B₃ characterizes a rather large ratio of P₅ /P₁₇, and Line OA₁ A₂ A₃C characterizes a ratio of P₅ /P₁₇ which is equal to 1.

The segments OA always identify the first phase of operation andrepresents the same pressure scales on ordinate and abscissa linesegment which is inclined at 45°.

The second phase of operation always starts at the points A1, A2 or A3.The applicable characteristic bends at this point upward from the 45°line since the pressure P₁₀ in this phase of operation is greater thanthe pressure P₅. The pressure P₁₀ increases along the deflected linesegment AB to the supply pressure P₂₇ at points B1, B2, B3 or C, andremains on this level while P₅ continues to increase.

The illustration shows that the larger the ratio P₅ /P₁₇, the firstphase of operation extends in the direction of increasing values forpressure P₅, and for identical control pressures (P₅ /P₁₇ =1) there isessentially no excess of the working pressure P₁₀ resulting from thedesign compared to the control pressure P₅, i.e., the embodimentillustrated in FIG. 1 behaves sort of like a universal relay valve.

Even when the relay valve is controlled only with the control pressureP₅, it behaves like a universal relay valve, and releases a workingpressure P₁₀ which is essentially identical to the designed pressure(45° line).

In the case of an increase or decrease in the supply pressure, thepoints B would lie on lines parallel to the abscissa characterizing thenew supply pressure, and the salient Points A would be shifted to higheror lower control pressures P₅. An example of such a case is plotted witha dotted line in FIG. 2, a lower supply pressure P'₂₇ with thecorresponding points A'₁ B'₁.

The position of the salient Points A is determined by the ratio of thecontrol pressures to one another, or by the absolute value of the supplypressure, or by the ratio of surface areas on the graduated piston 16,24, 25. The slope of the deflected branch of the characteristic curves,i.e., the segments AB, can be determined in advance by the ratio ofsurface areas between the step surface 32 and the second control surface21 of the graduated piston 16, 24, 25, and is the same for all ratio ofP₅ /P₁₇.

When pressure P₅ decreases, the characteristic curves described aboveapply in the opposite direction.

As shown in FIG. 3, the working pressure versus the second controlpressure is exhibited by the series of plotted curves.

The working pressure is again symbolized by P₁₀ and is plotted on theordinate. The second control pressure is again symbolized by P₁₇ and isplotted on the abscissa. A line parallel to the abscissa at the intervalof the supply pressure P₂₇ again identifies the supply pressure which isrespresented as constant.

In this illustration, the first phase of operation is characterized bythe segment OD on the abscissa, i.e., in the first phase of operation,no working pressure at all is released. In the second phase ofoperation, working pressure P₁₀ increases from Point D along the lineDF, is identical at the intersection E with the 45° line to the secondcontrol pressure P₁₇, and at Point F reaches the level of the supplypressure P₂₇ . When there is a further increase in pressure P₁₇, thepressure P₁₀ remains on the level of the supply pressure P₂₇.

Assuming identical pressure scales, the slope of the segment DFcorresponds to that of the segment AB in FIG. 2, and can be determinedin advance in the same manner as described above.

When the supply pressure P₂₇ changes, the Points F move correspondinglyon the line parallel to the abscissa at a distance to the same, and thePoints D and E in the same direction with the supply pressure P₂₇ to newvalues for the second control pressure P₁₇. For example, the lowersupply pressure P'₂₇ is plotted as the dotted line in FIG. 3 with thecorresponding Points D', E' and F', whereby the slope of the segmentD'E'F' is identical to that of the segment DEF.

The characteristic curves of FIGS. 2 and 3 illustrate that under normalconditions, in which the relay valve and the control pressure source arefed from the same reservoir, the supply pressure can be releasedsecurely and, depending on the extent of the ratio of surface areasbetween the graduation surface 32 and the second control surface 21, canbe rapidly and gradually released in proportion to the working pressure.In an embodiment not illustrated, in which the reaction force on thegraduated piston is produced by a control biasing spring, the remarksmade regarding the characteristic curves in FIGS. 2 and 3 applyaccordingly, except that the remarks concerning the case of the modifiedsupply pressure P₂₇ do not apply.

The characteristic curves also give an impression that the relay valve,shown in FIG. 1, has many possible applications in machine tools or inrailroad gate controls.

The response characteristics illustrated in FIG. 2 of the behavior ofthe embodiment, illustrated in FIG. 1, of the ratio of the controlpressures to one another makes this relay valve particularly suited forapplications in pneumatic brake installations for vehicles in which,independent of the control ratio of a load-controlled brake forcecontroller, above a predetermined control pressure, the available supplypressure must be able to be exerted as the braking pressure. In thiscase, the predetermined control pressure is used for the definition ofan emergency situation, or it can be called on for that purpose.

Referring to FIG. 4, there is shown a schematic illustration of apneumatic brake installation for vehicles which utilizes a relay valvein accordance with the present invention.

The reference numbers of the various connections of the relay valve,shown in FIG. 1, have been used in FIG. 4. This Figure shows a pneumaticbrake installation having a reservoir 50, a brake valve 51, aload-controlled brake force controller with a contraction apparatus,namely ALB 53, a brake cylinder 55, and a relay valve 56.

The reservoir 50 is in communication with an input supply connection ofthe brake valve 51 as well as with the supply connection 27 of the relayvalve 56.

The output of the brake valve 51 is in communication with the entranceconnection of the controller 53 and with the second control connection17 of the relay valve 56.

The output 54 of the load-controlled brake force controller 53 is incommunication with the control connection 5 of the relay valve 56.

The working connection 10 of the relay valve 56 is in communication withthe brake cylinders 55.

In the description of the operation of this vehicular brake application,it is assumed that the functions of the pedal brake valve 51, theload-controlled brake force controller 53, the brake cylinder 55, andthe relay valve 56 are all well-known.

When the brake valve 51 is actuated by the operator of the vehicle, theinput 52 of the load-controlled brake force controller 53 is pressurizedfrom reservoir 50 and is proportionally reduced to correspond to thecontrol ratio which is set as a function of the load and, in turn, isconveyed to the relay valve 56 at the first control connection 5.

However, full pressure released by the brake valve 51 is directlyconveyed to the relay valve 56, namely, to second control connection 17.

Under the action of these two pressures, namely, the first controlpressure and the second control pressure, the operation of the relayvalve 56 proceeds in the manner indicated in the descriptions of FIGS. 1and 2.

It is apparent that the pneumatic brake application can also be equippedwith a load-controlled brake force controller which is a more economicalmodel in the pressure-reducing feature and may be omitted from theapparatus.

The action of the pneumatic brake system of FIG. 4 will be describedwith reference to FIG. 5, which is a schematic representation of aportion of the family of characteristic curves which are capable ofbeing produced by the apparatus.

The brake pressure available at the brake cylinders 55 is symbolized byP_(B) and is plotted along the ordinate. The control pressure releasedby the brake valve is symbolized by P_(S) and is plotted along theabscissa. A line parallel to the abscissa represents the supplypressure, which is symbolized by P_(V) and which is assumed to beconstant. The following remarks refer to a relay valve according to theinvention, which in the first phase of operation as a result of thedesign, the work pressure P₁₀ released is essentially identical to thecontrol pressure P₅. For models which have a different characteristic inthe first phase of operation, the following remarks apply withadaptations which will be apparent to a specialist in the field.

The segment OH represents the initial response characteristic during theintroductory entrance control phase. In this phase, the brake pressureP_(B) is essentially identical with the control pressure P_(S). With thesame pressure scales on the ordinate and abscissa, the segment OH runsat an angle of 45° to both coordinates.

During the subsequent control phase, the control characteristic for thefully-loaded vehicle is deflected in the direction of a lower value forbrake pressure P_(B) from the 45° line with H as the salient point,whereby the control characteristics are represented by a bundle of lineswhich eminate from the Point H.

One of the bundle of lines of the control characteristic for an unloadedvehicle is line HK₁, for a partly-loaded vehicle is line HK₂, and for afully-loaded vehicle is line HK₃. All of the response curves omit theeffects of dynamic axle load shifts.

The characteristic curve HK₃ for the fully-loaded vehicle is essentiallyan extension of the entrance characteristic curve OH in that the controlpressure P_(S) is essentially equal to the full brake pressure P_(B).The Point K₃ is the modulation point, at which the brake pressure P_(B)is the same as the supply pressure P_(V), and beyond which the brakepressure P_(B) can no longer be increased.

During the advanced control phase which follows the subsequent controlphase, the load-dependent control characteristics HK, with the exceptionof the one for the fully-loaded vehicle, are deflected sharply in thedirection of higher brake pressures P_(B) and run steeply on a newcharacteristic to the modulation Point K₃. In the advanced controlphase, the line K₁ K₃ is the control characteristic for the unloadedvehicle, and the line K₂ K₃ is the control characteristic for thepartly-loaded vehicle. The characteristics for the vehicle with otherload statuses bend correspondingly, while the salient points always lieon the line K₁ K₃.

The position of the salient Points K can be determined in advance by thesurface area ratios on the graduated piston 16, 24, 25 of the relayvalve 56, and is also a function of the absolute value of the supplypressure, and to an extent determined by the slope of the line K₁ K₃ ofthe control ratio set by the load-controlled brake force controller 53.The slope of the line K₁ K₃ can be determined in advance by theabove-mentioned ratio of surface areas.

If there is a reduction or an increase in the supply pressure to thevehicle, the beginning of the advanced control phase is shifted to loweror higher values for control pressures P_(S). One example of such acase, in which the supply pressure is reduced, is characterized by thedotted line segment K'₁ K'₂ K'₃. In this case, the supply pressure whichis once again assumed to be constant, has dropped to a value P'_(V). Thebeginning of the advanced control phase is thereby shifted for theunloaded vehicle from the control pressure P_(S), identified by PointK₁, to a lower value characterized by Point K'₁. The Points K' of theother load-dependent control characteristics, e.g. K'₂, and themodulation Point K'₃, are correspondingly shifted.

The advanced control phase of the pneumatic brake installationcorresponds to an emergency situation. Referring to FIG. 5, there isshown that in this emergency situation, regardless of the control ratioof the load-controlled brake force controller 53 and regardles of theabsolute value of the supply pressure, the available supply pressure israpidly, controllably, and securely released as the brake pressure tothe brake cylinders 55. The family of characteristic curves for apneumatic brake arrangement not illustrated, in which theload-controlled brake force controller does not have an entrance device,the above remarks apply correspondingly, with the exception that Point Hforms the point of origin of the coordinate system.

For a brake installation with a relay valve 56, as described by theinvention in an embodiment not illustrated, in which the restoring forceon the graduated piston is produced by a control spring, the remarksmade concerning the family of characteristic curves of FIG. 5 applyaccordingly, with the exception that when the supply pressure P_(V)drops, the salient Points K are not shifted to lower values for controlpressures P_(S). This means that in these embodiments, an advancedcontrol phase can only occur so long as the supply pressure is higherthan the control pressure P_(S) corresponding to the salient point ofthe control characteristic in question. In such a brake installation,therefore, the emergency situation is defined by the absolute value ofthe control pressure P_(S).

Referring now to FIG. 6, there is illustrated a schematic representationof a relay valve with means engaging the relay piston for the initiationand control of the second phase of operation.

The components, connections, and chamber having the same function areagain identified by the same reference numbers as in FIG. 1.

As shown, a control chamber 4 is located above the relay piston 70 whichis connected with the control connection 5, and a reaction chamber 1 islocated below the relay piston 70 which is connected with the workingconnection. Located below the relay piston 70 is the double valve 6, 7,9.

In this embodiment, the relay valve 70 is designed as a differentialpiston with a large upper control surface 71 and a smaller lowerreaction surface 75. The differential surface 72, which accounts for thedifference in surface areas between these surfaces, is also situated onthe bottom of relay valve 70.

The reaction surface 75 of the relay piston 70 borders the reactionchamber 11. Between the differential surface 72 and the housing 73 isdefined a differential chamber 81 which is in communication with thesecond control connection 17 via a housing duct 80 and a pressure reliefvalve 77, 78.

The pressure relief valve 77, 78 includes a valve element 78, which isresiliently biased toward its closed position by a closing spring. Thepressure relief valve includes a valve seat 77 which is integral withthe housing.

Located coaxial to the pressure relief valve 77, 78 is the housing wallof a supply chamber 74 connected with the supply connection 27. Thesupply chamber is designed as a graduated bore in which a graduatedpiston 76 moves longitudinally, which is guided in a sealed manner. Thegraduated piston 76 has a small surface 82 which borders the supplychamber 74, and has a large surface 79 which faces the pressure reliefvalve 77, 78. The valve element 78 is activated by means of atappet-like extension.

The movement of the graduated piston 76 toward the pressure relief valve77, 78 is limited by a housing stop 75a.

A safety stop 80a is disposed in the control chamber 4 to limit theupward movement of the relay piston 70.

In the following explanation of the function of the embodimentillustrated in FIG. 6, let us assume that the supply connection 27 isconnected to a suitable pressure reservoir, that the working connection10 is connected with the consumer or consuming device, and that thefirst control connection 5 and the second control connection 17 areconnected to first or second control pressure sources, respectively.

It will be appreciated that there is a multitude of possible embodimentsof the control pressure and that the remarks and explanation relating tothe embodiment of FIG. 1 correspondingly apply in the present instance.

In the rest position, the control chamber 4, the reaction chamber 11,and the differential chamber 81 are exhausted to atmosphere. Thegraduated piston 76 is pressurized by the supply pressure and is urgedagainst the housing stop 75a. Thus, the pressure relief valve 77, 78 isin its open position.

It will be appreciated that the operating characteristics of the subjectembodiment are dependent on the ratio of the first control pressure inrelation to the second control pressure. In the following explanation,the same symbols used for FIGS. 2 and 3 will be used again.

If there is no second control pressure P₁₇, i.e., if P₁₇ /P₅ =0, thenthe working pressure P₁₀ is higher than the first control pressure P₅ inaccordance to the ratio of the control surface 71 of the relay piston 70to its reaction surface 75.

When the ratio P₁₇ /P₅ increases, the ratio between the working pressureP₁₀ and the control pressure P₅ becomes smaller. For a ratio P₁₇ /P₅ =1,the working pressure P₁₀ and the control pressure P₅ are essentiallyequal.

For the ratio P₁₇ >P₅, the working pressure P₁₀ is reduced or loweredfrom the first control pressure P₅.

If only a second control pressure P₁₇ is applied, then a lockingfunction occurs for the working pressure P₁₀. In this case, anundesirable large displacement of the relay piston 70 upward isprevented by the safety stop 80a.

In the embodiment illustrated in FIG. 6, there is a variable controlcharacteristic, which normally extends from a pressure-reducing to apressure-increasing characteristic.

The characteristic determined by the specified ratio of surface areas onthe relay piston 70 and the applicable pressure ratio P₁₇ /P₅ isdirected in the direction of higher working pressures P₁₀ up to theavailable supply pressure, when the second control pressure P₁₇ reachesthe limit pressure of the pressure relief valve 77, 78.

At this time, the force exerted by the supply pressure on the smallsurface 82 of the graduated piston 76 is overcome by the second controlpressure P₁₇ acting on the large surface 79 of the graduated piston 76.The graduated piston 76 is now moved away from the housing stop 75a andinto the supply chamber 74, whereby the pressure relief valve 77, 78closes under the action of the biasing spring. The slope of thecharacteristics above the salient point is determined by the ratio ofsurface areas on the relay piston 70. If the supply pressure decreasesor increases, the salient points are correspondingly shifted to lower orhigher values for the second control pressure P₁₇.

From the numerous variable operating characteristics of the embodimentillustrated in FIG. 6, it is apparent to the specialist in the fieldthat this can also be applied in numerous ways in different areas ofapplication.

The embodiment illustrated in FIG. 6 can also be used with a relay valve56 in the pneumatic brake installation illustrated in FIG. 4.

In a family of characteristics illustrated in FIG. 5, the characteristicof this embodiment is represented so that, by contrast to the embodimentillustrated in FIG. 4, the geometric location of the salient point is aline parallel to the ordinate at the interval of the limit pressure ofthe pressure relief valve 77, 78. Each control characteristic runs fromits salient point with the slope determined by the ratio of surfaceareas on the relay piston 70 to the 45° line upward, and after itreaches it, continues up to the available supply pressure. The bundle oflines therefore forms, on each side of the salient points, a bundle ofparallel straight lines which, after reaching the 45° line, are joinedon it.

If the supply pressure decreases or increases, the geometric location ofall the lines parallel to the ordinate forming salient points will alsoshift in the direction of lower or higher values for the controlpressure P_(S). From this shifted starting basis on, the brakinginstallation once again exhibits a characteristic which corresponds tothat described above.

It will be apparent to a specialist in the field that for the control ofthe pressure relief valve 77, 78, in place of the graduated piston 76, acontrol spring can also be used. In this case, with a changing supplypressure, the lines parallel to the ordinate forming the geometriclocation of all the salient points will not shift, and its positionwould therefore be dependent only on the absolute value of the controlpressure.

It will be apparent to the specialist in the field that the embodimentillustrated here, and any other form of a relay valve as described bythe invention, can also be used in installations using pressure fluidsother than air.

In another model of an embodiment (not shown), the differential chamber81, instead of being connectable to the second control connection 17,can be connected by means of a valve with the reaction chamber 11. Thevalve is controlled by a graduated piston, which is pressurized on itslarge surface by the second control pressure, on its small surface bythe working pressure from the reaction chamber 21, and on thedifferential surface with the supply pressure.

The valve and thus the communication between the differential chamber 81and the reaction chamber 11 is opened, as long as the sum of the forcesfrom the supply pressure and working pressure on the graduated pistonexceeds the force exerted on the latter by the second control pressure.

The valve and thus the communication between the differential chamber 81and the reaction chamber 11 is closed, if the force exerted by thesecond control pressure on the graduated piston exceeds the sum of theforces exerted by the supply pressure and the brake pressure on thegraduated piston.

The second phase of operation of this modified embodiment starts withthe closing of the valve. For the characteristics of this embodiment,the remarks made with regard to the examples illustrated in FIGS. 1 and4 and the family of characteristics illustrated in FIGS. 2, 3 and 5apply fully.

Thus, the present invention has been described in such full, clear,concise and exact terms as to enable any person skilled in the art towhich it pertains to make and use the same, and having set forth thebest mode contemplated of carrying out this invention. We state that thesubject matter, which we regard as being our invention, is particularlypointed out and distinctly claimed in what is claimed.

It will be understood that variations, modifications, equivalents andsubstituttions for components of the above specifically-describedembodiment of the invention may be made by those skilled in the artwithout departing from the spirit and scope of the invention as setforth in the appended claims.

Having thus described our invention what we claim as new and desire tosecure by Letters Patent, is:
 1. A relay valve for a pneumatic brakeinstallation for vehicles, comprising:(a) an inlet valve having acontrol connection which is pressurized with a control pressure andhaving at least one supply connection which is pressurized by supplypressure and which is put in communication with at least one workingconnection; (b) an outlet valve for connecting the working connection tothe atmosphere; (c) said inlet valve and said outlet valve beingoperated by a relay piston which can be pressurized by the controlpressure to move the inlet valve in the opening direction and to movethe outlet valve in the closing direction and being operated by therelay piston which can be pressurized in the closing direction by theworking pressure supplied to a reaction chamber which is connected tothe working connection to move the inlet valve and in the openingdirection to move the outlet valve; (d) means which provides a graduatedincrease of the working pressure beyond the value corresponding to thedelivered control pressure, up to the available supply pressure; and (e)said means is activated above a predetermined pressure value of a secondcontrol pressure.
 2. A relay valve for a pneumatic brake installationfor vehicles, comprising:(a) an inlet valve having a control connectionwhich is pressurized with a control pressure and having at least onesupply connection which is pressurized by supply pressure and which isput in communication with at least one working connection; (b) an outletvalve for connecting the working connection to the atmosphere; (c) saidinlet valve and said outlet valve being operated by a relay piston whichcan be pressurized by the control pressure to move the inlet valve inthe opening direction and to move the outlet valve in the closingdirection and being operated by the relay piston which can bepressurized in the closing direction by the working pressure supplied toa reaction chamber which is connected to the working connection to movethe inlet valve and in the opening direction to move the outlet valve;(d) means which provides a graduated increase of the working pressurebeyond the value corresponding to the delivered control pressure, up tothe available supply pressure; (e) said means is activated above apredetermined pressure value of a second control pressure; (f) saidinlet valve and outlet valve are formed by a double valve with a doublevalve element; and (g) said means is actively associated with said relaypiston.
 3. The relay valve, according to claim 2, wherein:(a) said relaypiston is designed as a differential piston having a large controlsurface and a smaller reaction surface and a differential surface; (b) adifferential chamber is located between the differential surface and thehousing which can be pressurized by means of a pressure relief valvewith the second control pressure; and (c) said pressure relief valve iscontrolled by a graduated piston pressurized with the second controlpressure on its small surface and with the supply pressure on its largesurface for closing, so that the pressure in the differential chamber islimited to a value determined by the ratio of surface areas on thegraduated piston.
 4. A relay valve for a pressure fluid systemcomprising:(a) An inlet valve connecting at least one supply connectionwith at least one working connection when a control connection ispressurized with a control pressure; (b) an outlet valve for connectingthe working connection to the atmosphere; (c) said inlet valve and saidoutlet valve being operated by a relay piston, the relay piston beingacted upon by the first control pressure in the opening direction of theinlet valve and in the closing direction of the outlet valve and beingacted upon by a working pressure supplied to a reaction chamber in theclosing direction of the inlet valve and in the opening direction of theoutlet valve; (d) said relay piston is designed as a differential pistonhaving a large control surface and a smaller reaction surface and adifferential surface; (e) a differential chamber is located between thedifferential surface and the housing which can be pressurized by meansof a pressure limiting valve with a second control pressure supplied toa second control connection; and (f) said pressure limiting valve iscontrolled by a graduated piston pressurized with the supply pressure onits small surface and pressurized with the second control pressure onits large surface until the limiting valve closes so that the pressurein the differential chamber is limited to a value determined by theratio of surface areas on the graduated piston.